Field of the Invention
This invention relates to communication systems; and more particularly, to a tunable logarithmic amplifier, systems incorporating the same, and an improved method of signal reception in radios using a tunable logarithmic amplifier.
Description of the Related Art
Radio based communication systems contain transmit and receive sub-systems, with the receive sub-system tasked with receiving small amplitude signals which are quite often close to the noise level that is present in the receiver. These radio based communication systems are becoming more common in society as the use of cell phones and Wi-Fi systems along with radio based Machine to Machine (M2M) become more prevalent. Advances in noise figure reduction in Low Noise Amplifiers (LNAs) along with signal processing techniques have improved the sensitivity of radios. A need for continued improvements in receiver sensitivity will require advances in other technologies or architectures in the receiver sub-system.
One of the main limiters of receiver sensitivity is the quality of the LNA, since this provides the first stage of amplification for the weak signals being received. A class of amplifier that is used in receivers is a logarithmic amplifier (termed a “log amp”), with the log amp having the characteristic of providing an output signal that is proportional to the logarithm of the input signal. The logarithmic relationship between input and output signals of the amplifier provide for the ability to amplify small input signals without amplifying the noise present at the amplifier input port. A common method of achieving a log amp topology is to connect multiple gain blocks in series. Such a topology provides the logarithmic function at the expense of dynamic range and bandwidth.
A more recent configuration, as described by Rada et al. in US 2015/0070058, published Mar. 12, 2015 (“the '058 pub”), has been developed is termed a logarithmic detector amplifier (LDA) system and consists of an amplifier circuit configured to receive an input signal and generate an oscillation based on the input signal, a sampling circuit coupled to the amplifying circuit and configured to terminate the oscillation based on a predetermined threshold to periodically clamp and restart the oscillation to generate a series of pulses modulated by the oscillation and the input signal, and one or more resonant circuits coupled with the amplifying circuit and configured to establish a frequency of operation and output an RF signal; the contents of the '058 pub. are hereby incorporated by reference. This circuit configuration, as described in the '058 pub., can result in improved frequency selectivity which results in higher sensitivity compared to a standard log amp. This circuit topology, however, also suffers from reduced bandwidth and dynamic range.
There is a long felt need for a receive system that provides the benefits of a logarithmic amplifier along with improved bandwidth and dynamic range to accommodate radio systems that need to cover multiple and wider frequency ranges. Along with these improvements there is also a need to provide dynamic optimization of receive performance of a radio system for mobile devices and devices where the environment or propagation channel changes during the course of operation, for example, the changes to the performance of the radio incurred when a smartphone is placed in the users' hand and then placed next to the head.